ext4: add MODULE_SOFTDEP to ensure crc32c is included in the initramfs

Fixes: a45403b5 ("ext4: always initialize the crc32c checksum driver")
Reported-by: François Valenduc <francoisvalenduc@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org